It looks to me like the backpack doesn’t have kinematic collision. Each bone seems to have this collision (as it should), but the backpack doesn’t presumably because there’s no bone specifically for the back pack. That’s fine though since you could probably just expand the size of one of the spine bones’ collisions. Just enough to keep the hair away from the back pack.
To be honest, the clipping issue doesn’t look bad from the images alone in my opinion.